Captain Ben Brown’s rapid 61 took Sussex to 447 for 8 before they declared their first innings against Derbyshire at Hove.
Brown struck eight fours and a six from 54 balls before he was bowled by Matt Critchley, the first of two wickets for the leg spinner who had Ajmal Shahzad caught at long off for seven before Sussex declared with a lead of 297.
Derbyshire openers Billy Godleman and Chesney Hughes negotiated seven overs before lunch to take their side to 12 for 0.
Earlier, Luke Wells was out to the third ball of the day after failing to add to his overnight 104. Wells was caught behind to give Ben Cotton a deserved first wicket while Tony Palladino had Harry Finch (16) caught behind attempting to run the ball down to third man after he added 53 in ten overs with Brown.